Process for increasing the concentration of normal paraffins in a light naphtha stream

Abstract

A process increases the concentration of normal paraffins in a feed stream comprising separating a naphtha feed stream into a normal paraffin rich stream and a non-normal paraffin rich stream. A naphtha feed stream may be separated into a normal paraffin stream and a non-normal paraffin stream. An isomerization feed stream is taken from the non-normal paraffin stream and isomerized over an isomerization catalyst to convert non-normal paraffins to normal paraffins and produce an isomerization effluent stream. The isomerization effluent stream may be separated into a propane stream and a C4+ hydrocarbon stream optionally in a single column. The C4+ hydrocarbon stream may be recycled to the step of separating a naphtha feed stream.

The invention claimed is: 
     
       1. A process for increasing the concentration of normal paraffins in a feed stream comprising:
 separating a naphtha feed stream into a normal paraffin stream and a non-normal paraffin stream comprising C 5  and C6 non-normal paraffins and less than about 0.5 wt % cyclic hydrocarbons; 
 isomerizing the non-normal paraffin stream over an isomerization catalyst at a temperature in a range from about 225 to 260° C. to produce an isomerization effluent stream; 
 separating said isomerization effluent stream into a propane stream and a C4+ hydrocarbon stream wherein said isomerization effluent stream has a normal/iso ratio of about 1-1.7; and 
 recycling said C4+ hydrocarbon stream to said naphtha feed stream for separation of the normal paraffins from the non-normal paraffins, 
 wherein said isomerization effluent stream comprises C 2 -C 6  normal paraffins to methane selectivity ratio of about 40-55 based on weight, wherein the isomerization is conducted at a liquid hourly space velocity (LHSV) of about 4 to 7.5 h −1 , and wherein said isomerization feed stream has an inlet mole ratio of H 2 /hydrocarbon of about 0.5 to 0.6. 
 
     
     
       2. The process of  claim 1  wherein said C4+ hydrocarbon stream is a C4-C6 hydrocarbon stream. 
     
     
       3. The process of  claim 1  wherein said isomerization zone maintains a pressure in the range of 450-650 psig. 
     
     
       4. The process of  claim 1  wherein said isomerization zone produces about 30-65 Wt % C 2 -C 6  normal paraffins. 
     
     
       5. The process of  claim 3  wherein said effluent stream has a light paraffins (C2-C3) to C 2 -C 6  normal paraffins selectivity of about 50-60% based on weight. 
     
     
       6. The process of  claim 1  wherein a molecular weight ratio of said isomerization effluent stream to said isomerization feed stream is about 0.70 to 0.80. 
     
     
       7. A process for treating a naphtha feed stream comprising:
 separating a naphtha feed stream into a normal paraffin stream and a non-normal paraffin stream comprising C 5  and C 6  non-normal paraffins and less than about 0.5 wt % cyclic hydrocarbons; 
 isomerizing the non-normal paraffin stream over a chlorided alumina catalyst at a temperature in a range from about 225 to 260° C. to produce an isomerization effluent stream; 
 separating said isomerization effluent stream with a depropanizer column into a depropanizer overhead stream comprising propane and a depropanizer bottoms stream comprising C4+ paraffins; and 
 recycling said depropanizer bottoms stream comprising C4+ paraffins to said naphtha feed stream for separation of the normal paraffins from the non-normal paraffins, 
 wherein said isomerization effluent stream comprises a C 2 -C 6  normal paraffins to methane selectivity ratio of about 40-55 based on weight, wherein the isomerization is conducted at a liquid hourly space velocity (LHSV) of about 4 to 7.5 h −1 , and wherein said isomerization feed stream has an inlet mole ratio of H 2 /hydrocarbon of about 0.5 to 0.6.